The invention relates generally to rolls for treating webs of material and, more particularly, to an improved sealing arrangement for a hydraulically supported roll.
A hydraulically supported roll having a rotatable hollow cylinder forming the working roll circumference and a stationary crosshead extending lengthwise through the hollow cylinder to form a surrounding clearance space with the inner circumference of the hollow cylinder is disclosed in DE-PS No. 31 28 140. External forces for supporting the roll are applied to the ends of the crosshead that project from the hollow cylinder, which is supported on the crosshead by hydraulic fluid in the clearance space. Transverse end seals, designed as clearance seals, are provided between the hollow cylinder and the crosshead to seal the ends of the clearance space. The transverse end seals have radially extending, flat surfaces that are maintained at a spacing from each other, independent of relative displacement between the crosshead and the hollow cylinder, by a roller bearing having a bearing ring that forms one of the flat surfaces.
The hollow cylinder disclosed in the above-mentioned document is supported for rotation relative to the crosshead by bearings mounted on the ends of the crosshead. At each of these ends, a ring is fixedly attached to the hollow cylinder at the inner side of the bearing for rotation with the hollow cylinder. This ring simultaneously forms one of the flat surfaces of the clearance seal and one of the bearing rings of the roller bearing. The other bearing ring of the roller bearing carries the other flat surface, which is parallel to the first flat surface and is spaced opposite it at a small clearance of less than 0.1 mm, generally in the range of 0.02 mm. The other bearing ring does not rotate, but rather is fixed with the crosshead; however, this ring is axially displaceable to the small degree required. The compression in axial direction is effected by circumferentially distributed compression springs that are supported on an extension of the crosshead.
Rolls of the type discussed above are generally designed as hydraulically supported, so-called "swimming rolls". In these rolls, longitudinal seals extend at diametrically opposite sides of the crosshead between the transverse end seals, and together with the transverse end seals, define a somewhat semi-cylindrically-shaped longitudinal chamber, which is pressurizable with hydraulic fluid. When pressurized, the fluid in the longitudinal chamber supports the hollow cylinder. In addition, other types of hydraulic devices for supporting the hollow cylinder, such as those in which the transfer of forces from the crosshead to the inner circumference of the hollow cylinder is effectuated by separate hydrostatic supporting elements distributed along the length of the hollow cylinder, are contemplated with the present invention. In these types of rolls, the clearance space remaining between the crosshead and the inner circumference of the hollow cylinder may be filled with hydraulic fluid. To prevent discharge of this fluid, a seal must be provided. Further, although the invention is applicable primarily to rolls having hollow cylinders fixedly supported by bearings, the invention also is applicable to those rolls in which the hollow cylinder can execute what is known as "inner lift", as is disclosed in DE-AS No. 22 54 392.
The present invention arose in connection with the problems that occurred when especially high line pressures had to be transmitted, at high hydraulic fluid temperatures, by the longitudinal chamber of supported swimming rolls of the type discussed above. Under these conditions, pronounced deflections of the crosshead and, thus, pronounced changes in the angle of the crosshead relative to the inner circumference of the hollow cylinder occurred in the area of the transverse end seals, in addition to especially pronounced axial displacements of the hollow cylinder relative to the crosshead, because of the difference in the coefficients of thermal expansion of the hollow cylinder and the crosshead. Because the first gap defining surface of the transverse end seal of the type disclosed in DE-PS 31 28 140 is mounted on the hollow cylinder, the transverse end seal also undergoes both the considerable axial displacements and the pronounced angular changes of the hollow cylinder. This causes problems such as one-sided loading of the rolling elements of the roller bearings, which maintain the spacing between the first and second surfaces, and wear and tear of the seal located between the first bearing ring of the roller bearing and the crosshead.